As a method for safely managing secret information, a management method is known whereby secret information is distributed to users by employing a threshold secret sharing scheme, and whereby the secret information can be restored by collecting the information from not less than a predetermined number of users to whom the information was previously distributed, based on user IDs and passwords (see, for example, Japanese Patent Laid-Open Publication No. 2003-333028).
Further, as a method whereby a server and a user verify and certify each other, a certification method is known that employs independent component analysis (see, for example, Japanese Patent Laid-Open Publication No. 2005-31730).